In a heat pump and refrigeration cycle, refrigerant alternately absorbs and rejects thermal energy as it circulates through the system and is compressed, condensed, expanded, and evaporated. In particular, a liquid refrigerant flows from a condenser, through an expansion device (e.g., expansion valve) and into an evaporator. As the refrigerant flows through the expansion device and evaporator, the pressure of the refrigerant decreases, the refrigerant phase changes into a gas, and the refrigerant absorbs thermal energy. From the evaporator, the gaseous refrigerant proceeds to a compressor, and then back to the condenser. As the refrigerant flows through the compressor and condenser, the pressure of the refrigerant is increased, the refrigerant phase changes back into a liquid, and the refrigerant gives up thermal energy. The process is implemented to emit thermal energy into a space (e.g., to heat a house) or to remove thermal energy from a space (e.g., to air condition a house). To summarize, a heat pump is an air conditioner that reverses the process of removing heat from the inside of the house (e.g., during summer) to absorbing the heat from outside air and moving it inside (e.g., during winter).
A heat pump is usually effective by itself down to temperatures around 25 to 30 degrees Fahrenheit. At lower temperatures, a gas furnace or auxiliary electric heat may be used to assist the heat pump. In other words, a heat pump may operate simultaneously with auxiliary electric heat. Additionally, the auxiliary electric heat may also be used as emergency heat in the event a heat pump needs service.
Under normal operating conditions, auxiliary electric heat is activated automatically by the thermostat when the indoor temperature drops during heat pump operation. There are also times during cold, wet weather when the outdoor coil may ice up and the heat pump will go into a defrost cycle. The defrost cycle reverses the heating process (i.e., the air conditioning process is activated) causing the outdoor coil to heat and melt any ice. The defrost cycle may last a few minutes and then the heating process is activated again. During the defrost cycle, the auxiliary electric heat may be activated since the heat pump is producing cold air at the internal coil.
The heat elements and other components used for auxiliary electric heat operations have a limited lifespan. Thus, efforts to improve the performance/durability of components for auxiliary electric heat operations and/or to decrease their frequency of use are desirable.